Infection of 3T3 cells with SV40 results in a malignant transformation of a certain percentage of these cells. Present experimental evidence indicates that the SV40 genome is integrated into cellular DNA in the transformed cell. A procedure designed to isolate intermediates in the integration process is described. Benzoylated naphoylated DEAE cellulose chromatography will be used to fractionate those viral DNA molecules possessing an altered secondary structure in infected 3T3 cells. This DNA can then be analyzed, along with replicating cellular DNA, by velocity and equilibrium centrifugation. An experimental approach is presented which is designed to test the hypothesis: Is cellular DNA synthesis required for transformation. Chromatographic and cell fractionation techniques are suggested which may lead to the elucidation of several intermediate steps in the transformation process.